Process for preparing thiophenes

Abstract

Preparation of a thiophene by the action of H 2 S on an organic substance containing oxygen or sulphur. The substance which is used is an unsaturated carbonyl or thiocarbonyl compound, particularly an aldehyde, thioaldehyde, ketone or thioketone. The reaction preferably takes place between 250° and 500° C. on a catalyst of the alumina type containing an alkali or alkaline earth oxide. The process permits the unsubstituted or substituted thiophene to be obtained with high yields and high degrees of selectivity, exceeding 70%.

We claim: 
     
       1. A method for preparing thiophenes, which comprises reacting in the presence of an alumina catalyst between 250° and 500° C. hydrogen sulfide with a compound selected from the group consisting of the unsaturated carbonyl and thiocarbonyl compounds represented by the formula ##STR11## where X is O or S while each of the symbols R, R', R" and R''' is hydrogen or lower alkyl, or ortho-tolualdehyde or phenyl-acetaldehyde, then condensing the reaction mixture and separating the thiophene formed. 
     
     
       2. Method according to claim 1 wherein the reaction is carried out at about 300° C. to about 400° C. 
     
     
       3. Method according to claim 1, wherein the compound selected is crotonaldehyde. 
     
     
       4. Method according to claim 1, wherein the compound selected is mesityl oxide. 
     
     
       5. Method according to claim 1, wherein the compound selected is methylethyl acrolein. 
     
     
       6. Method according to claim 1, wherein the compound selected is 3-penten-2-one. 
     
     
       7. Method according to claim 1, wherein the compound selected is 2-methyl-2-butenal. 
     
     
       8. Method according to claim 1, wherein the compound selected is 2-n.hexenal. 
     
     
       9. Method according to claim 1, wherein the compound selected is 2-ethyl-2-hexenal. 
     
     
       10. Method according to claim 1, wherein the alumina used as catalyst contains γ alumina. 
     
     
       11. Method according to claim 10, wherein the alumina is incorporated with 0.5 to 15% by weight of a compound selected from the group consisting of Na 2  O, K 2  O, Na 2  S and K 2  S. 
     
     
       12. Method according to claim 11, in which the catalyst has a specific area in the range of about 60 to about 350 m 2  /g. 
     
     
       13. Method according to claim 12, in which the reaction is carried out under a pressure of 1 to 10 bars. 
     
     
       14. Method according to claim 1, wherein the amount of hydrogen sulfide is about 2 to about 5 moles per mole of said selected compound. 
     
     
       15. Method according to claim 11, wherein the amount of hydrogen sulfide is about 2 to about 5 moles per mole of said selected compound.